In lead frames used for the assembly of LED-related products, a bright silver plating is typically plated on a copper lead frame, or a bright silver plating is plated on a nickel plating layer such that the nickel plating layer is located between the bright silver plating layer and the copper lead frame.
FIG. 1 illustrates prior art plating schemes for the manufacture of bright silver LED devices. A first typical prior art plating scheme for a lead frame 100 comprises a base copper substrate 104 which is plated with copper to form a copper layer 106 over the base copper substrate 104. The copper layer 106 is further plated with a bright silver layer 108 comprising silver.
A second typical prior art plating scheme for a lead frame 102 comprises a base copper substrate 104 which is plated with copper to form a copper layer 106 over the base copper substrate 104. Nickel is then plated over the copper layer 106 to form a nickel layer 110 on top of it. Finally, the lead frame 102 is plated with a bright silver layer 108 on top of the nickel layer 110.
For both plating schemes used to fabricate the respective lead frames 100, 102, copper plating is applied on the surface of the base copper substrate 104 prior to conducting bright silver plating or nickel plating onto the lead frame surface.
In the typical plating schemes described above, it has been found that silver or silver ion migration occurs on the bright silver layer 108. Such silver or silver ion migration is a major problem because it causes tarnishing of the bright silver layer 108, leading to a decrease in the lumen or emission of visible light from the LED device. The foregoing events deteriorate LED performance in the final product.